1. Field
Apparatuses and methods consistent with exemplary embodiments relate to a power supplying apparatus, a power supplying method, an organic light-emitting diode (OLED) display apparatus, and more particularly, to a display apparatus including an OLED and a method of supplying power thereto.
2. Description of the Related Art
The development of electronic technology has brought the development and supply of various types of electronic products. In particular, various types of display apparatuses, such as a TV, a portable phone, a personal computer (PC), a notebook PC, a personal digital assistant (PDA), etc., are used in most general homes.
A conventional display apparatus displays various types of images by using a liquid crystal display (LCD). The conventional LCD is not a self-emission display apparatus and thus uses a backlight unit as a light source.
In general, a display apparatus rectifies a commercial voltage of 110 V or 220 V applied from an external source and supplies the rectified commercial voltage to power consumption parts of the display apparatus. Since a backlight unit requires a driving voltage higher than the other power consumption parts, the display apparatus is to separately include a main DC-DC converter which is to supply power to the backlight unit and a sub DC-DC converter which is to supply power to the other parts.
Therefore, a conventional LCD requires additional cost, and the display apparatus is limitedly made slim and light. Also, the conventional LCD requires backlight and thus is heavy and thick and has a slow response speed.
An organic light-emitting display has been developed as a next generation image display apparatus replacing an LCD. The organic light-emitting display displays an image by using organic light-emitting diodes (OLEDs) which emit light through a recombination of electrons and holes.
Here, each of the OLEDs of the organic light-emitting display includes an anode, a cathode, and an emission layer formed between the anode and the cathode. Also, if a current flows from the anode to the cathode, the emission layer emits light, and an amount of the light varies according to changes of an amount of the current, thereby representing luminance.
The organic light-emitting display using the above-described OLEDs has a high color representation and a thin thickness. Therefore, the organic light-emitting display has wide application in a portable phone, a PDA, an MP3 player, etc.
A method of driving the organic light-emitting display using the OLEDs is greatly classified into a passive matrix method and an active matrix method. The passive matrix method refers to a method of orthogonally forming an anode and a cathode and applying a current to selected cathode and anode lines to drive the anode and the cathode. The active matrix method refers to a method of integrating a thin film transistor (TFT) and a capacitor into each pixel to maintain a voltage due to a capacitance of the capacitor.
A process of driving an organic light-emitting display including general OLED pixels by using an active matrix method will now be described with reference to FIG. 1.
FIG. 1 is a circuit diagram illustrating a process of driving a conventional organic light-emitting display by using an active matrix method.
Referring to FIG. 1, the conventional organic light-emitting display includes OLEDs each including scan lines SL and data lines DL which cross each other, a switching transistor T1, a driving transistor T2, and a capacitor C. The switching transistor T1 includes a gate which is connected to the scan lines SL and a source which is connected to the data lines DL. The driving transistor T2 includes a gate which is connected to a drain of the switching transistor T1 and a source which is connected to a first power source ELVDD. The capacitor C is formed between the source and the gate of the driving transistor T2. A drain and an anode of the driving transistor T2 are connected to each other, and the source is connected to a second power source ELVSS.
A circuit operation of the organic light-emitting display will now be described. If the switching transistor T is turned on, a data voltage is applied to a gate electrode of the driving transistor T2. Also, a current flows in the OLED through the driving transistor T2 due to the data voltage to emit and display light. In addition, the data voltage applied to the gate electrode is maintained for a predetermined time due to the capacitor C.
An OLED as described above has low voltage and high current characteristics. Therefore, if a conventional power supply unit (e.g., a switch mode power supply (SMPS)) is applied, high power efficiency is not achieved.